Effect of extraction methods on the efficiency of sumac (Rhus coriaria L.) fruit extract in soybean oil quality during accelerated conditions

Abstract Herbal extracts containing natural bioactive substances with numerous beneficial effects have been recently noticed as appropriate alternatives for synthetic food preservatives. In this study, we aimed to optimize the effects of different sumac (Rhus coriaria) fruit extracts (SFE) on oxidative stability of soybean oil under accelerated conditions compared to a synthetic antioxidant. Hydro‐ethanolic extracts (70%) of sumac fruits were prepared by three methods of immersion (I‐SFE), ultrasound (U‐SFE), and microwave (M‐SFE). According to the response surface methodology (RSM), 13 runs were considered in the concentrations of 0, 500, and 1000 ppm of each extract that were added to the soybean oil and stored at 60°C for a 20‐day period. All of the treatments were significantly (p < .05) efficient in preventing the chemical and sensory changes of soybean oil compared to the control in the dose‐dependent manner during storage period. I‐SFE treatment showed the lowest peroxide value (PV) (0.000063 meq (milliequivalents) O2/kg oil), thiobarbituric acid reactive substances (TBARS) (115.06 MDA (malondialdehyde)/kg oil), and acid value (0.0169 mg KOH (potassium hydroxide)/kg oil) among the other extracts at the end of the storage period. Furthermore, I‐SFE treatment earned the highest sensory scores (flavor, color, odor, and overall acceptability) of soybean oil in the range of 4–5 in comparison to the other treatments and synthetic antioxidant during storage time. According to the analysis of RSM, I‐SFE in the concentration of 999.998 ppm could optimally enhance the shelf life of soybean oil for 11.3614 days under accelerated conditions. It was concluded that I‐SFE with the same efficiency as synthetic antioxidants can be considered as a suitable alternative in soybean oil with various health benefits.


| INTRODUC TI ON
Soybean is widely used for the manufacture and formulation of edible oil in many countries. Soybean oil is rich in polyunsaturated fatty acids (PUFA), disposed to the oxidation phenomenon and free radical production during storage period or under heat conditions, such as frying and cooking. Lipid oxidation is one of the spoilage reactions in foods that can lead to the quality and customer-friendliness loss. Food manufacturers are forced to use synthetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), to combat lipid oxidation phenomenon; but, they are not sure about the safety effects of these compounds on consumer health. These concerns always exist about the use of synthetic additives in food (Tinello & Lante, 2020;Umeda & Jorge, 2021). The recent research introduced natural replacements for solving this problem. Herbal extracts and essential oils with numerous beneficial effects can be appropriate choices (Bagheri et al., 2016;Javadian et al., 2017). Most of these plants are found in many areas of the world and in addition to antioxidant and therapeutic properties, they can improve the sensory features, such as taste, odor, color, and overall acceptability of the food. Therefore, these agrofood products can be used for producing functional foods (Basturk et al., 2018;Tinello & Lante, 2020;Umeda & Jorge, 2021). Sumac plant with the scientific name of Rhus coriaria L., belonging to the Anacardiaceae family, grows widely from Mediterranean to Iran and Afghanistan. In many countries, sumac fruit powder is served with various foods as a pleasant and popular condiment. Previous studies have demonstrated antioxidant activities of sumac fruit extract in laboratory conditions and food models. They reported that sumac fruit extracts contain phenolic acids, flavonols, anthocyanins, hydrolyzable tannins, and organic acids, such as malic, citric, and tartaric acids (Alsamri et al., 2021).
Extraction method can significantly affect the release amount of the bioactive substances in the extracts. Therefore, depending on the extraction method, the produced extract will have different physicochemical properties (Geow et al., 2021). Immersion-assisted extraction method is the traditional solid-liquid extraction technique, in which the sample is placed in contact with the solvent at room temperature for long time with shaking until the bioactive phytochemicals present in the sample particles are completely solubilized and then released in the solvent (Azwanida, 2015;Geow et al., 2021). Ultrasound and microwave-assisted extraction methods are the novel extraction approaches for the extraction of the bioactive substances of the plants. Ultrasound-assisted extraction method creates the acoustic cavitation phenomenon in the solvent by the ultrasonic wave transition, which ruptures the cell membranes and enhances the contact surface between the plant sample and solvent. Therefore, the solvent penetrates into the plant cells, followed by releasing the effective substances of the samples. The generated heat by the microwave-assisted extraction method has a great role in the yield of the phenolic compound extractions. This can be correlated to the high adsorption of microwave heat by the plant cell water, which leads to increasing water vapor pressure inside them, followed by the destruction of the cell wall and release of the phenolic compounds into solvent (Chemat et al., 2020;Sinan et al., 2020). In this regard, the objective of this work was to optimize and evaluate the effects of the produced sumac fruit extracts using three methods of immersion, microwave, and ultrasound at various concentrations on chemical (peroxide value (PV), thiobarbituric acid reactive substances (TBARS), and acid value (AV)) and sensory (flavor, color, odor, and overall acceptability) features of soybean oil stored at 60°C for 20 days compared to the synthetic antioxidant.

| Preparation of SFE
Sumac fruits were purchased from the local markets in Hamadan.
After grinding the samples in the grinder (Hardstone, United Kingdom), mixed aqueous ethanol (70%) solvent with the ratio of 1:10 was obtained and then extracted by immersion (I-SFE), ultrasound (U-SFE), and microwave (M-SFE) methods. In the immersion procedure, the samples were shaken in 250 rpm (revolutions per minute) for 24 hr. An ultrasound apparatus (FAPAN, Tehran, Iran) was used in the ultrasound method with the frequency of 20 kHz, the power of 50, and the temperature of 25°C for 30 min. In the microwave-assisted extraction, the samples were extracted in a microwave oven (SolarDOM, LG, Seoul, Korea) with the frequency of 2450 MHz for 30 min. Next, the obtained solutions were filtered and concentrated by a rotary evaporator apparatus (Lab Tech) at 40ºC. Then, the remaining solvent was removed by vacuum oven at 50°C. After drying, the extracts were stored at −18ºC for subsequent uses (Albu et al., 2004;Barkhordari & Bazargani-Gilani, 2021;Pan et al., 2008).

| Preparation of the treatments
The fresh refined soybean oil, free of chemical antioxidants, was provided from an oil factory. The treatments were prepared in three groups, including: 1. SFE 0 ppm (soybean oil free of SFE), 2. SFE 500 ppm (soybean oil containing 500 ppm of SFE), and 3. SFE 1000 ppm (soybean oil containing 1000 ppm of SFE) for all three extracts. Tween 80 was used in 0.2% concentrations as an emulsifier.
According to the design expert software, for these three groups, 13 runs were considered for all extracts separately that are defined in Table 1. Furthermore, soybean oil containing 200 ppm BHT was considered as the positive control. In other words, a total of 40 treatments were designated. All of the treatments were subjected to the accelerated test in an oven at 60 ± 1°C for 20 days and evaluated at 0, 10, and 20 days of storage period (Tinello & Lante, 2020;Umeda & Jorge, 2021).

| Peroxide value
Peroxide value (PV) was measured by the method suggested by the International Dairy Federation (IDF) (Shantha & Decker, 1994). PV was expressed as milliequivalents (meq) of O 2 per kg of oil.

| Thiobarbituric acid reactive substances (TBARS)
The thiobarbituric acid reactive substances (TBARS) value was measured according to the Iranian National Standards (10,. A standard curve was determined using 1,1,3,3-tetraethoxypropane (TEP) and the data were considered as milligrams (mg) of malondialdehyde (MDA) per kilogram (kg) of oil.

| Acid value
Acid values (AVs) of the samples were evaluated on the basis of the International Standard ISO (660-2009). AV was reported as milligrams (mg) of potassium hydroxide (KOH) per kilogram (kg) of oil.

| Statistical analysis
Response surface methodology (RSM) was used for the efficiency optimization of all three SFEs on the quality of stored soybean oil.
For this purpose, central composite design in three levels and five repetitions in the central point were considered for the evaluation of SFE effects on the physicochemical and sensory characteristics of the heated soybean oil during storage time (+1, 0, −1) ( Table 2). In this study, the independent variable limits, such as the concentrations of SFE and storage time, were found by the primary tests. Also, the obtained data were statistically analyzed by SPSS software (IBM SPSS statistics 21) and reported as mean values ±standard deviations (SD). The analysis of variance (ANOVA) and Tukey test were used at the significance level of p <.05 to compare the means.

| PV
The unstable free radical molecules made from triglycerides during oxidation reaction are called peroxides. Peroxides are tasteless and odorless molecules but decompose rapidly to hydro-peroxides, followed by aldehyde compounds, which have strong unpleasant taste and odor. PV determines the produced peroxides as the primary products of oxidation reaction in the oils (Tinello & Lante, 2020).
According to Figure 1a, by increasing the storage period of the treatments, an ascending trend of PV was observed until the 15th day.
After that, a declining pattern appeared in PV until the end of the storage period. This can be correlated to decomposing unstable peroxides TA B L E 1 Designated treatments by design expert software analysis for each extraction method to secondary products of lipid oxidation, such as aldehydes during accelerated storage of the samples. According to Figure 1b, by increasing the storage period, an ascending trend in the TBARS value of all studied samples was observed.
In the first 10 days of the storage period, due to the peroxide formation in the initiation phase of lipid oxidation, the TBARS index showed low increase; while, in the second 10 days of the storage, by decomposition of peroxides to hydro-peroxide and then more stable compounds, such as aldehyde and ketone products, the TBARS index exhibited the highest value for all treatments. Figure  in various classes of phytochemicals, including flavonoids, tannins, polyphenolic compounds, organic acids, and many others. According to the previous studies, the remarkable antioxidant activity of the sumac fruit ethanolic extract can be related to the high content of the bioactive substances such as gallicin, gallic acid, glucogallic acid, quercitrin, isohyperoside, myricetin glucuronide, tri-galloylhexoside, penta-galloyl-hexoside, myricetin rutinoside, dihydroxymethyl xanthone, β-sitosterol-hexoside, α-tocopherol, and linoleic acid compounds (Abdallah et al., 2019). According to the reports of another study, sumac fruit extract and sumac-synthesized nanoparticles exhibited reducing power and significant (p <.05) scavenging activity against DPPH and ABTS (2,2'-azinobis-(3-ethylbenzothiaz oline-6-sulfonic acid) free radicals (Bursal & Koksal, 2011;Ibrahim et al., 2019;Majd et al., 2017). Salimi et al. (2015) showed that the sumac fruit aqueous extract (50, 100, and 200 mg/kg) decreased malondialdehyde (MDA), a marker of oxidative stress, in the alloxaninduced diabetic rats.

| AV
The AV (acid value) is milligram of the required potash to neutralize the free fatty acids in 1 gram of oil. This index measures the acidity content and therefore the quality of the oil (Mahesar et al., 2014). Figure 1c illustrates with the peroxide and TBARS values of the samples, the significant differences of AV were expected to be observed among the studied treatments during storage period (Wang et al., 2018). This may be correlated to the low accuracy of the titration method to find these differences. AV of the oils is measured by a titration method in an organic solvent, such as ethanol; then, potassium hydroxide (KOH) solution is used to titrate the acids in oil to a targeted pH end point. The presence of the organic solvent leads to a high mix of oil with the titrant, as a result of which the neutralization reaction will occur very quickly. Due to the weak and low content of fatty acids in the oils, finding a sharp pH end point in titration is unattainable.
As a result, the measurement error for AV analysis will be inevitable. Therefore, a simple, efficient, and accurate method for the determination of acid value in edible oils has been recently recommended by a solvent-assisted and reaction-based headspace gas chromatography (HS-GC), Fourier-transform infrared (FTIR) spectroscopy, and spectrophotometric methods (Mahesar et al., 2014;Xie & Chai, 2016).

| Optimum storage conditions
According to the obtained findings and design expert software analysis (Table 3)

| CON CLUS ION
It was concluded that SFE was effective in decreasing the chemical and sensory changes, followed by increasing the shelf life of the soybean oil during accelerated storage. This property of SFE was significantly affected by the kind of the extraction method, so that the immersion-assisted extraction method was the most efficient technique in releasing the antioxidant substances in the solvent among the other methods and the ultrasound and microwaveassisted extraction methods were in the next ranks, respectively.  Overall acceptability Maximum 2 2 2 5 5 5 Abbreviations: AV, acid value; PV, peroxide value; TBARS, thiobarbituric acid reactive substances.
F I G U R E 5 (a-c) The optimized storage conditions of the soybean oils containing I-SFE (a), U-SFE (b), and M-SFE (c) under accelerated conditions. I-SFE, immersion-assisted extraction method-sumac fruit extract; U-SFE, ultrasound-assisted extraction method-sumac fruit extract; and M-SFE, microwave-assisted extraction method-sumac fruit extract

ACK N OWLED G EM ENTS
This study was supported by the Faculty of Veterinary Science, Bu-Ali Sina University, Hamedan, Iran.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

E TH I C A L A PPROVA L
This study does not involve any human or animal testing.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data available on request from the authors.